Designing
UiO-66-Based Superprotonic Conductor with
the Highest Metal–Organic Framework Based Proton Conductivity
Subhabrata Mukhopadhyay
Joyashish Debgupta
Chandani Singh
Rudraditya Sarkar
Olivia Basu
Samar K. Das
10.1021/acsami.9b01121.s001
https://acs.figshare.com/articles/journal_contribution/Designing_UiO-66-Based_Superprotonic_Conductor_with_the_Highest_Metal_Organic_Framework_Based_Proton_Conductivity/7926794
Metal–organic framework (MOF)
based proton conductors have
received immense importance recently. The present study endeavors
to design two post synthetically modified UiO-66-based MOFs and examines
the effects of their structural differences on their proton conductivity.
UiO-66-NH<sub>2</sub> is modified by reaction with sultones to prepare
two homologous compounds, that is, <b>PSM 1</b> and <b>PSM
2</b>, with SO<sub>3</sub>H functionalization in comparable extent
(Zr:S = 2:1) in both. However, the pendant alkyl chain holding the
−SO<sub>3</sub>H group is of different length. <b>PSM 2</b> has longer alkyl chain attachment than <b>PSM 1</b>. This
difference in the length of side arms results in a huge difference
in proton conductivity of the two compounds. <b>PSM 1</b> is
observed to have the highest MOF-based proton conductivity (1.64 ×
10<sup>–1</sup> S cm<sup>–1</sup>) at 80 °C, which
is comparable to commercially available Nafion, while <b>PSM 2</b> shows significantly lower conductivity (4.6 × 10<sup>–3</sup> S cm<sup>–1</sup>). Again, the activation energy for proton
conduction is one of the lowest among all MOF-based proton conductors
in the case of <b>PSM 1</b>, while <b>PSM 2</b> requires
larger activation energy (almost 3 times). This profound effect of
variation of the chain length of the side arm by one carbon atom in
the case of <b>PSM 1</b> and <b>PSM 2</b> was rather surprising
and never documented before. This effect of the length of the side
arm can be very useful to understand the proton conduction mechanism
of MOF-based compounds and also to design better proton conductors.
Besides, <b>PSM 1</b> showed proton conductivity as high as
1.64 × 10<sup>–1</sup> S cm<sup>–1</sup> at 80
°C, which is the highest reported value to date among all MOF-based
systems. The lability of the −SO<sub>3</sub>H proton of the
post synthetically modified UiO-66 MOFs has theoretically been determined
by molecular electrostatic potential analysis and theoretical p<i>K</i><sub>a</sub> calculation of models of functional sites
along with relevant NBO analyses.
2019-03-19 00:00:00
3 H proton
UiO -66-based MOFs
alkyl chain attachment
proton conduction mechanism
MOF-based proton conductors
3 H functionalization
side arm
3 H group
length
pendant alkyl chain
UiO -66 MOFs
proton conductors
NBO
PSM 1
PSM 2
Designing UiO -66-Based Superprotonic Conductor
proton conductivity
side arms results
UiO -66-NH 2
post synthetically
activation energy